Polyester polyurethane lacquers from mixed phthalic acids

ABSTRACT

POLYURETHANE LACQUER COMPOSITION WHICH COMPRISES A SOLVENT SOLUTION OF A POLYMER PREPARED BY REACTING AN ALIPHATIC POLYISOCYANATE WITH AN HYDROXYL POLYESTER OF AN EXCESS OF A POLYHYDRIC ALCOHOL WITH A MIXTURE OF PHTHALIC ACID AND HEXAHYDROPHTHALIC ACID.

U.S. Cl. 260-29.1

United States Patent 3,554,951 POLYESTER POLYURETHANE LACQUERS FROMMIXED PHTHALIC ACIDS Friedrich Blomeyer, Cologne-Stammheim, WilhelmBunge,

Leverkusen, Gerhard Mennicken, Opladen, and Reinhard Hebermehl,Leverkusen, Germany, assignors to Farhenfabriken BayerAktiengesellschaft, Leverkusen, Germany, a corporation of Germany NoDrawing. Continuation of application Ser. No. 535,025, Mar. 17, 1966.This application Mar. 26, 1969, Ser. No. 812,958 Claims priority,application Germany, Mar. 17, 1965,

Int. Cl. C08g 22/06, 22/10, 51/26 7 Claims ABSTRACT OF THE DISCLOSUREPolyurethane lacquer composition which comprises a solvent solution of apolymer prepared by reacting an aliphatic polyisocyanate with anhydroxyl polyester of an excess of a polyhydric alcohol with a mixtureof phthalic acid and hexahydrophthalic acid.

This application is a continuation of application Ser. No. 535,025,filed Mar. 17, 1966, now abandoned.

This invention relates to polyesters and polyurethane plastics based onpolyesters. More particularly the invention relates to polyestercompositions that have improved properties, particularly for theproduction of certain types of polyurethanes.

It has been proposed heretofore to prepare polyurethanes from polyesterswhich are based on phthalic acid and a polyhydric ,alcohol. It has beenalso proposed.

heretofore to prepare polyurethane plastics which are based on aliphaticpolyisocyanates. The polyurethane plastics based on aliphaticpolyisocyanates, particularly hexamethylene diisocyanate and its urea orbiuret derivatives, and polyesters based on phthalic acid retain theirgloss and color tone even under adverse conditions. The beststabilization of color tone and gloss are obtained if certain polyestersbased on phthalic acid and trimethylolpropane are reacted with a biuretisocyanate of the type disclosed in U.S. Pat. 3,201,372. When apolyester, for example one prepared from phthalic acid andtrimethylolpropane, having a hydroxyl number of 225 to 270, is reactedwith a biuret triisocyanate, films are obtained which do not show anyloss of gloss or any change in color tone after being exposed for fouryears to salt water, high altitude climates or industrial atmospheres.Furthermore, these polyester coatings have excellent resistance tosynthetic tests. For example, they show no loss of gloss after 2000hours in the weatherometer. This excellent resistance to weathering andexposure to the elements have not been obtained herefore using any otherpolyhydroxyl compound, even in conjunction with the biurettriisocyanate. It has been found, however, that the polyesters based onphthalic acid alone or indeed in a mixture with other .acids such amaleic acid and the like exhibit unsatisfactory compatability withadditives and unsatisfactory solubility in solvents which must be usedin order to deposit polyurethane coating compositions onto substrates.Due to this incompatibility gel particles form prematurely and it ispractically impossible to deposit a perfectly smooth coating on a steelsubstrate, for example. Furthermore, the polyesters which give thesehighly advantageous properties are incompatible with many of the usualadditives such as flow improvement agents, thickeners and the like,which are customarily employed in the preparation of coatingcompositions. Since the polyester has limited solubility in the solventsand limited compatibility with the flow improving agents and thickenersbased on cellulose, polyesters or hydrogenated castor oils their use,for example, for automotive coatings and the like has heretofore beenimpractical. Another disadvantage of the heretofore known coatings basedon phthalic acid and even mixtures of phthalic acid with other acids isthat the polyester has only limited solubility with aromatic solventssuch as toluene and xylene.

It has been proposed heretofore to prepare polyurethane plastics basedon polyesters from hexahydrotereph thalic acid alone. These polyestersresult in films which have inadequate resistance to solvents.

It is, therefore, an object of this invention to provide polyurethanesand polyesters for the preparation of polyurethanes which have improvedcompatibility with other components in polyurethane formulations andimproved solubility insolvents, particularly aromatic solvents, whichare used in order to apply a film to a substrate. Another object of thisinvention is to provide particular mixtures of acids which areadvantageous for the preparation of improved polyesters and particularlyimproved polyurethane plastics based on said polyesters which aredeposited on a substrate by evaporation of .a solvent. A further objectof this invention is to provide polyurethane plastics, particularlycoatings which are more uniform, free of lumps and surface defects andwhich are stable against the influence of additives, particularly thosebased on cellulose, hydrogenated castor oil, polyesters and the like.Still another object of this invention is to provide polyesters andpolyurethanes coating compositions based on those polyesters which haveimproved solubility in solvents used for the production of coatingcompositions and particularly aromatic solvents. A further object ofthis invention is to provide for the preparation of polyesters and toprovide for the preparation of polyurethanes based on the polyesterswhich have improved properties.

The foregoing objects and others which will become apparent from thefollowing description are accomplished in accordance with the invention,generally speaking, by providing hydroxyl polyesters which are based ona mix ture of phthalic acid and a hexahydrophthalic .acid reacted withan excess of polyhydric alcohol and polyurethanes prepared by reactingsaid polyesters with an organic polyisocyanate. The inventioncontemplates polyurethane coating compositions based on organicpolyisocyanates of many types, however, where the polyester is to beemployed in the production of a coating composition which is to haveimproved gloss and improved compatibility with the other compounds, itis preferred to use an aliphatic polyisocyanate, most preferably onewhich contains additional urea, biuret or isocyanurate groups.

The polyesters of the invention are prepared by reacting a mixture ofphthalic acid and a hexahydrophthalic acid in proportions of from about0.5 to .about 2.5 mols of phthalic acid to about 2.5 to 0.5 mols ofhexahydrophthalic acid. The compatability of the polyesters with theadditives and solvents used in the preparation of polyurethane films isincreased with increasing contents of a hexahydrophthalic acid, but toomuch will result in poor resistance to solvents. Polyester-s based onproportions of phthalic acid and a hexahydrophthalic acid in the rangeof 2:1 to 1:2 (molar) and an excess of polyhydric alcohol based oncarboxylic acid groups or mixtures of .acid is especially advantageouswith regard to compatibility. While the invention is particular tophthalic acid, i.e. benzene-1,2 dicarboxylic acid, it is possible to mixin isophthalic acid, i.e. benzene-1,3-dicarboxylic .acid, in place of aportion of the phthalic acid. Good solubility combined with goodcompatibility with polymers and copolymers is obtained if, for example,the ratio of phthalic acid to isophthalic acid to hexahydrophthalic acidis 1:1:1.

Any suitable hexahydrophthalic acid may be used such as lower alkylhexahydrophthalic acid such as, for example:

l-methylcyclohexane-2,3-dicarboxylic acid,1-ethylcyclohexane-2,3-dicarboxylic acid,1-propylcyclohexane-2,3-dicarboxylic acid,l-butylcyclohexane-2,3-dicarboxylic acid, as well as1-methylcyclohexane-3,4-dicarboxylic acid,1-ethylcyclohexane-3,4-dicarboxylic acid,1-propylcyclohexane-3,4-dicarboxylic acid,1-butylcyclohexane-3,4-dicarboxylic acid, endomethylenehexahydrophthalic acid, i.e.

and the like. The term phthalic without modification refers throughoutto the ortho acids and not to meta or para acids. Furthermore, both thecis and trans isomers are contemplated, where appropriate. The acids areprepared, for example by hydrogenation of the corresponding aromaticacids or they can be prepared by the Diels- Alder condensation, forexample of maleic anhydride and butadiene, isoprene or cyclopentadienewith simultaneous hydrogenation.

Any suitable alcohol may be used for the preparation of the polyester ofthe invention, but it is preferred to use diols or triols. Suitablepolyhydric alcohols include the lower alkylene glycols having theformula HO (C H2 O) H where n is from 2 to 10, such as for example,ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, l,4-butanediol, 1,3-butane diol, 2,3-butane diol, pentaglycol, 1,6-hexanediol,2,3-hexanediol, 1,7-heptanediol, 1,8-octane diol, 1,9-nonane diol.Suitable triols include, for example, glycerine, trimethylol propane,1,3,6- hexane triol and the like. The polyhydric alcohols Preferablyhave a molecular weight below about 500.

The polyesters are prepared, for example by mixing the acids with thepolyhydric alcohol and gradually heated, preferably in an inertatmosphere of nitrogen, argon and the like, preferably to 200 to 220 C.depending on the rate at which water is split off. The reaction ispreferably first carried out at atmospheric pressure and subsequentlyunder a partial vacuum to aid in removing the water of condensation. Ifdesired, the esterification may be carried out with the use of a carrieror in the presence of an esterification catalyst such as sodium,potassium, lithium, calcium, magnesium, zinc, cadmium, manganese, iron,cobalt, nickel, tin, lead and bismuth as well as the carbonates, oxidesand alcoholates of alkaline and alkaline earth metals either alone or incombination, zinc chloride, aluminum chloride, antimony chloride,antimony fluoride, boron fluoride, the oxides, chlorides, sulfates,acetates, alcoholates and salts of higher aliphatic or aromaticmonocarboxylic acids of the elements of the third, fourth and secondsub-group of the periodic system, alkaline and/or alkaline earth metalsalts of silicic acid, stannic acid, selenic acid, phosphoric acid andtungstic acid or the like. Especially valuable catalysts are manganesephosphate, mixtures or manganese phosphate and antimony oxide, ormixtures of manganese phosphate, antimony oxide and zinc acetate. Theproportion of the mixture of acids to alcohol should be such that therewill be an excess of hydroxyl groups present so that hydroxyl polyestersare obtained.

The polyester of the invention can be reacted with an organicpolyisocyanate to prepare polyurethane plastics particularly films whichare deposited from a solvent and which have improved high gloss andresistance to weathering. Moreover the color tone of the polyurethaneplastics of the invention are improved by the use of the polyhydricpolyesters disclosed above. One of the most important advantages of theinvention is that the polyesters do not form gel particles which show upin the coatings as rough places on the surface.

Any suitable organic polyisocyanate may be used for the preparation ofthe polyisocyanate plastics of the invention. It is preferred, however,to use aliphatic polyisocyanates such as hexamethylene diisocyanate,ethylene diisocyanate, trimethylene diisocyanate, tetramethylenediisocyanate, decamethylene diisocyanate, 1,4-cyclohexane diisocyanate,1-methyl-2,4-diisocyanato cyclohexane, l-methyl 2,6-diisocyanatocyclohexane and mixtures thereof. In addition it is often preferred touse isocyanates which are based on reaction products of the monomericisocyanates with other components in order to increase their molecularweight and functionality. For example, organic isocyanates which containurea, biuret, isocyanurate or acyl groups are particularly advantageousfor the preparation of improved coatings in accordance with the presentinvention. Biuret polyisocyanates of this type are disclosed, forexample in U.S. Pat. 3,201,372, particularlyN,N',N"-tris-(isocyanatohexyl)-biuret, N,N',N"-tris-(isocyanatobutyl)-biuret, N,N,N"-tris-(isocyanatobutyldiisocyanatophenyl)-biuret,N,N',N"-tris-(4-isocyanatocyclohexyl)-biuret,N,N,N"-tris-(isocyanatobenzyl)- biuret, N,N',N"-tris(betaisocyanatoethylbenzene)-biuret, N-4-isocyanatophenyl N',N"-di- (isocyanatobutyl -biuretas well as higher biuret polyisocyanates which may be represented by theformulas:

| NCO and the like. Examples of isocyanaurate polyisocyanates of thoseobtained, for example by trimerizing hexamethylene diisocyanate,tetramethylene diisocyanate, xylylene- 1,4- or 1,3-diisocyanate eitheralone or with additional isocyanates includingtoluylene-2,4-diisocyanate and the like, in the presence of a suitabletrimerization catalyst such as trialkylphosphine, for example,trimethylphosphine, triethylphosphine, tribenzylphosphine and the like.It is also possible to use isocyanates which contain acyl groups, forexample isocyanates obtained by reacting an aliphatic diisocyanate withan aliphatic dicarboxylic acid. Any of the aliphatic diisocynatesreferred to above may be reacted with any suitable dicarboxylic acid,such as adipic acid, methyl adipic acid, glutaric acid, methyl glutaricacid, phthalic acid, hexahydrophthalic acid and the like. There must beat least four mols of organic diisocyanate present per mol ofdicarboxylic acid.

In comparison with the heretofore known phthalic acid polyesters thepolyesters of this invention have outstanding solubility in solvents andoutstanding compatibility with the usual additives used in thepreparation of polyurethane lacquers. Solutions of the polyisocyanates,even where there are high portions of aromatic solvents such as xyleneor toluene can be prepared. The preferred solvents contain less than 60percent by weight aromatic solvents and most preferably less thanpercent aromatic solvents. Suitable solvents and mixtures of solventsare shown in Table 1. Furthermore, the polyesters of the invention arecompatible with flow improving agents such as cellulose, esters andethers and linear polymers of vinyl acetate, polyvinyl acetate,polyvinyl butyral, hydrogenated castor oil and the like as well asgelling agents from bentonite and montmorillonite. Their compatibility 6siloxane, catalysts, such as zinc octoate, stannous octoa-te, triethylamine and the like if any of these additives are necessary or desirablefor the particular application.

The polyurethanes prepared according to the invention are usefulpreferably for coating compositions where with nitrocellulose isoutstandingly good. resistance to weather, color tone, high permanentgloss -In order to determine the compatibility of the polyand the likeare required. For example, for the top coat esters of the invention withsundry combinations of 801- in painting automobiles, for corrosionresistant industrial vents reference is made to the following Table Iwherein coats on metal, wood and the like. They are particularlypolyesters which were prepared by heating the indicated distinguished bytheir high abrasion resistance and high mixtures of acids and alcoholsin an inert atmosphere of resistance to chemicals. The coatingcompositions of the nitrogen to a temperature of about 200 to about 220C. invention may be employed where air drying or oven drywhile removingthe water of condensation until the indiing is desirable. cated hydroxylnumber is obtained, are mixed with the The invention is furtherillustrated 'by the following various solvents shown in Table I with theresults that are examples in which parts are given by weight unlessotherindicated. Where numerals are used to indicate the soluwisespecified. bility the indication is in parts per hundred parts of sol-The isocyanates employed are prepared as follows: vent. Isocyanate1.Sutiicient hexamethylene diisocyanate is TABLE I Polyester 1 2 3 4 5solutions with butyl acetate; Ethglgne glycol monoethyletheracetate/xylene solutions 25 A, solutions l (a) (4) 4 4 Ethyllene glycolmonoethyl other acetate/xylene 50% solutions (o (o (o (o 25% solutionsEthylene glycol monoethyl e er acetatezbutyl acetatezethylacetateztoluene= 1:12

50% solutions 25% solutions (t) (l) (4 50% solutions are treated with10% solutions 6 of cellulose acetobutyrate (43% butyric acid)(K-Value=50) 0.04 0.04 0. 04 0.04 Polyvinyl butyral 0. 05 0. 5 l. 2 0. 510. 0 Polyvinyl acetate... 0. 5 0. 6 0. 1 0.5 Nitrocellulose 40.0 40.040.0 40 0 Copolymers of vinyl acetate and vinyl chloride 0. 1 2. 0 10. 04. 0 10 0 30% solution was treated with copolymer of vinyl acetate andvinyl chloride 02 10.0 10.0 10.0 10 0 25% solution 1 was treated withcellulose acetobutyrate (43% butyric acid) (K-Value=70)- 1.0 100 10.010.0 100 Combination of polyesters l-5 with alkyd resin 2 in the ratioof 1:1:

60% solution a 25% solution 6 ethyl ketoneztoluenc in the proportions of3:1:

2 Short oil alkyd resin modified with saturated, low molecular weightfatty acid.

3 Insoluble.

4 Soluble.

5 Incompatible.

6 Compatible.

Numbers 6 limiting value of compatibility as percentage, based on thequantity of binder.

OH number Polyester 1 from 3 mols phthalic acid and 3.6 molstrimethylolpropane 290 Polyester 2 from 2 mols phthalic acid, 1 molhexahydrophthalic acid and 3.6 mols trimethylolpropane Polyester 3 from1 mol phthalic acid, 2 mols hexahydrophthalic acid and 3.6 molstrimethylolpropane Polyester 4 from 1 mol phthalic acid, 1 molhexahydrophthalic acid, 1 mol isophthalic acid, and 3.3

mols trimethylolpropane as well as 0.3 mol hexanediol Polyester 5 from 1mol phthalic acid, 2 mols methylhexahydrophthalic acid, and 3.6 molstrimethylolpropane 285 The preparation of the coating compositions ofthe invention is preferably carried out by combining the polyesters andany desired additives, such as fiow improving agents or the like with asolvent which preferably contains less than about 60 percent aromaticsolvents and then adding an organic polyisocyanate in such proportionsthat the overall NCO:OH ratio is from about 1.01 to about 1.2 andpreferably 1.1 to 1.2 and then the coating is applied to a substratewhere the solvent evaporates. The solution may contain pigments such astitanium dioxide, flow improving agents such as polyphenyl methyl mixedslowly with water by adding the water to the isocyanate so that areaction product of 3 mols of the hexamethylene diisocyanate with 1 molof water is obtained. The initial reaction mixture is heated for about 2to 3 hours With slow evolution of carbon dioxide at a temperature ofabout C. Then the temperature of the reaction mixture is increased tofrom about to about C. for about 4 hours. After filtering to remove theby-product urea polyisocyanates and heating to remove hexamethylenediisocyanate which is unreacted, a biuret triisocyanate product isobtained which corresponds to 3 mols of hexamethylene diisocyanatereacted with 1 mol of water. A 75 percent solution of this product in amixture of ethylene glycol monoethyl ether acetate and xylene (1:1) andhaving a NCO content of 17 percent is used.

Isocyanate 2.About 109.5 parts of adipic acid are introduced into about1000 parts of hexamethylene diisocyanate at about C. and heated forabout three hours, about 66 parts of carbon dioxide being split off;About 1030 parts of the reaction mixture are freed from excesshexamethylene diisocyanate at about C. and about 1.5 mm. Hg in athin-film evaporator and about 470 parts of a very viscouspolyisocyanate are obtained, about a 75 percent solution of which inethyl glycol monoethyl ether acetate and xylene (1:1) contains about 15percent of isocyanate groups and shows a dynamic viscosity of about 664cP/ 25 C.

Isocyanate 3.About 336 parts of hexamethylene diisocyanate (hydrolyzablechlorine 0.002%; total chlorine 8 content 0.05%) are treated with 1.2parts of tri-n-butylbe used for the preparation of the polyurethanesprovided phosphine and stirred for about 8 hours at about 50-60 that theteachings of this disclosure are followed. C. The NCO content has thendropped from 49.5% to Although the invention has been described inconsidera- 3536%. The reaction is stopped by the addition of about bledetail in the foregoing, it is to be understood that such parts benzoylchloride and heating briefly to 80 C. detail is solely for the purposeof illustration and that and the low viscosity liquid reaction productsis distilled f y variatiohs can be hy those Skilled in h art twice overa thin layer evaporator (vacuum 0.3 mm. Hg, Wlthoht deparhhg m the P andscope of the lhveh circulation temperature of the heating fluid 160-170C. hon except as Set forth In the dams" What is claimed is:

1. A lacquer composition which comprises a solvent solution of a polymerprepared by the process which comprises reacting an aliphaticpolyisocyanate with an hydroxyl polyester of an excess of a polyhydricalcohol with About 161 parts of distillate and about 170 parts ofpolymer having an NCO content of about is obtained. 10

Using these isocyanates as indicated in the following table and thepolyesters disclosed above as indicated after Table I and a solventmixture of ethylene glycol monoethyl a mixture of phthalic acid andhexahydmphthalic aCicL ether hcetate, butyl ficetate, methy1ethy 1kethe1 15 2. The lacquer composition of claim 1 wherein the lllene 1n the P Pof 331311 Coatlng Composltlons molar ratio of phthalic acid tohexahydrophthalic acid is were prepared as indicated in the followingTable II. in the range of 0.5 :2.5 to 2.5 :0.5.

TABLE II Polyester 1. Polyester 2. Polyester 3. Polyester 4. Polyester 5Polyester 6.

Epoxide resin. Solvent mixture Zinc octoate, 10% in solv is re 4 4 4Methylphenylsiloxane, 1% in solvent mixture 10 10 10 10 Titanium dioxiderutile (96) (102) (102) (98) Isoeyanatel 124 142 142 128 Isoeyanate 2Isocyanate 3 115 The value for titanium dioxide rutile is shown inparen- 3. The lacquer composition of claim 1 wherein the theses toindicate that experiments are carried out with molar ratio of phthalicacid to hexahydrophthalic acid is and without pigments which whenincorporated is incorin the range of 2:1 to 1:2. porated by trituration.The coatings are applied to steel 4. The lacquer composition of claim 1wherein the panels and then subjected to the weatherometer test andpolyhydric alcohol is a dihydric or trihydric alcohol havto freeexposure to weather in the ouside atmosphere. The ing a molecular weightbelow about 500. lacquers prepared according to Examples 1 to 7 show 5.The lacquer composition of claim 1 wherein phthalic no change in glossafter 2000 hours in the weatherometer. 4O acid, isophthalic acid andhexahydrophthalic acid are used Neither is there any change in colortone or is there any in the molar ratio of 1:1:1. evidence of chalking.This indicates two years possible 6. The lacquer composition of claim 1wherein the exposure to the outside elements. Lacquers preparedacaliphatic polyisocyanate is a biuret polyisocyanate. cording tocomparison example A begin to chalk and 7. The lacquer composition ofclaim 1 wherein the show a marked loss in gloss after only severalhundred polyester and the aliphatic polyisocyanate are reacted in hoursin the weatherometer which indicates that on exan inert organic solvent.posure to the outside atmosphere chalking and loss of gloss begin afteronly 1 /2 to 2 years. Lacquers prepared References Cited according tocomparison example B show marked loss of UNITED S A PATENTS gloss after500 hours in the weatherometer. The flow prop- 3,124,605 3/1964 Wagner260 453 erties of Examples 2 to 7 can be improved with auxihary 3 341498 9/1967 Skreckoski et al 260 75 agents where the flow properties ofthe lacquer of Example 92,183 7 /1968 Windemuth et 1 cannot.

It is to be understood that any other suitable acid or the DONALD E.CZAJA, Primary Examiner like could be used in the preparation of thepolyesters of the invention provided that the teachings of thisdisclosure S. COCKERAM Assistant Examiner are followed. It is also to beunderstood that any other US, Cl, X R, suitable aliphaticpolyisocyanate, solvent or the like could 26075, 77.5

